1. Technical Field
The invention relates to an apparatus for reproducing a digital audio signal from a record carrier, the record carrier having a first digital audio signal recorded on it in a first format and a second digital audio signal recorded on it in a second format, the apparatus comprising
read means for reading an information signal from the record carrier,
decoding means for channel decoding the information signal read from the record carrier into a decoded information signal,
input means for receiving a selection signal,
output means for supplying an output signal which comprises either the first digital audio signal or the second digital audio signal in response to said selection signal, said output means further being adapted to include an identification signal into said output signal, said identification signal indicating that said output signal comprises either said first digital audio signal or another audio signal, and to a method for reproducing said digital audio signal.
2. Related Art
An apparatus as defined in the opening paragraph is well known in the art in the form of a DVD video reproducing apparatus, such as described in the JEI, December 1996, the publication titled xe2x80x98Intriguing DVD technology opens broad possibilitiesxe2x80x99, pp. 21-25, document D1 in the list of related documents that can be found at the end of this description.
DVD video disks have a first digital audio signal stored on it in a first format, which is the well known linear PCM format. The first digital audio signal comprise the left and right hand signal components of a stereo audio signal. Further, the DVD disk has a second digital audio signal stored on it in a second format, which is in an MPEG encoded format. The second digital signal can be in a multi channel form and may comprise left and right hand signal components, as well as a centre signal component and one or two surround signal components.
The apparatus has an IEC 958 output interface for supplying the audio signals to an external decoder, which comprise a multi channel decoder for decoding the second digital audio signal into said signal components.
The invention aims at providing an improved reproduction apparatus. The reproducing apparatus in accordance with the invention further comprises
muting means for muting the first digital audio signal supplied by the output means in response to an occurrence of said selection signal for selecting said second audio signal, said muting means maintaining said output means in a muted situation from said moment of occurrence of said selection signal until a certain time interval after the corresponding change in said identification signal.
The invention is based on the following recognition. The prior art reproducing apparatus has the possibility to reproduce at least two digital audio signals. The first audio signal can be the audio signal that is encoded in linear PCM form. When reproducing the first digital audio signal, this audio signal is applied to the output means, such as the IEC 958 digital audio interface, and can be supplied to an external audio decoder apparatus. For decoding the linear PCM audio signal, the external apparatus comprise an D/A converter.
When switching over the prior art reproducing apparatus in a second reproduction mode, in which an MPEG encoded audio signal is reproduced, the MPEG encoded audio signal is supplied to the IEC 958 audio interface. The external apparatus further comprise an MPEG decoder in order to decode the MPEG encoded audio signal. Upon switching the prior art reproducing apparatus into the second reproduction mode, the information stream on the IEC 958 interface changes from a linear PCM encoded audio signal into an MPEG encoded audio signal. The external apparatus has to detect the change in contents of the information stream. This requires some time. During this time interval, however, the D/A converter receives information that it cannot decode. As a result, a severely distorted signal will be outputted by the external apparatus, which signal may destroy the loudspeakers coupled to the external apparatus.
By muting the audio signal supplied to the IEC 958 interface during the transition, it will be avoided that a severely distorted output signal will be generated by the external apparatus. This muting is realized by detecting the selection signal and generating a mute signal in response thereto. Further, the muting is maintained a certain time interval after the corresponding change in said identification signal. The identification signal is, in the example of the IEC 958 interface, the second bit (b1) in the channel status signal channel on the IEC 958 interface. This bit identifies the interface to be in a normal audio mode or in a xe2x80x98non-audio modexe2x80x99. In the xe2x80x98normal audio modexe2x80x99, the audio signal present on the interface is a linear PCM encoded audio signal, that can be decoded by a standard D/A converter in the external apparatus. When no linear PCM encoded audio signal, such as the MPEG encoded signal, is present on the interface, the interface is in the xe2x80x98non-audio modexe2x80x99. The length of the certain time interval identified above, has a relationship with the time interval that the external apparatus needs to detect the change in said identification signal.